Since keyboard device is the main input device in computer system, it has to conform to different developments and using demands of computer system due to the diversification of using environment and timing. For providing the user the positions of each key in a dark environment, a keyboard with illuminating capability is developed, such as U.S. Pat. No. 5,936,554, U.S. Pat. No. 7,278,750, TWP No. 566612 and TWP No. 581961, which respectively disclose a keyboard device with LEDs (Light Emitting Diode) mounted therein and each LED provides light for a single key, so that the keys can be clearly recognized in the dark. Although this kind of keyboard can prevent the incapability of recognizing the keys' positions in the dark, since the standard keyboard has more than one hundred keys and each key has to equip with the corresponding LED, the whole amount of components becomes much greater, the manufacturing process and cost are definitely increased and the weight even becomes larger. Besides, the power consumption and heat production owing to the large amount of LEDs also might influence the user.
Another kind of keyboard with illuminating capability is disclosed as U.S. Pat. No. 6,179,432, U.S. Pat. No. 6,199,996, U.S. Pat. No. 6,217,183, U.S. Pat. No. 6,284,988, U.S. Pat. No. 6,322,229, U.S. Pat. No. 6,554,442, U.S. Pat. No. 6,590,508, U.S. Pat. No. 6,648,530, U.S. Pat. No. 6,860,612, U.S. Pat. No. 7,235,752, U.S. Pat. No. 7,239,303, and U.S. Pat. No. 7,388,167, and TWP No. 509955, TWP No. 516671, TWP No. 587800, TWP No. 594546, TWP No. I230957, TWP No. I231693, TWP No. M240668, and TWP No. M313281. All these patents are related to additionally mount an illuminating plate, such as electroluminescent sheet, or optical fiber panel, above or under the bottom plate of the keyboard, so that the keys above the illuminating plate can shine for recognition. Compared with the keyboard which mounts the LEDs inside the keys, the keyboard using one single illuminating plate can shine uniformly and also can reduce the amount of components and facilitate the assembly. Besides, the low power consumptions of the electroluminescent sheet and the optical fiber panel are both low and are also advantageous to long term usage. Furthermore, TWP No. I269333 and U.S. application Ser. No. 11/288,258 also disclose a keyboard with back light architecture, wherein a light source transmitting space is defined between the plank and the bottom board and at least a light guiding portion corresponding to the light source on the keyboard portion toward the light source transmitting space is mounted on the plank, so that the light guiding portion can receive the light inputting the light source transmitting space and guide the light to the keyboard portion, thereby forming the back light architecture of the keyboard.